As an irrigation method, the inter-ridge irrigation and hose irrigation are performed. In recent years, the droplet irrigation technology has been proposed as a so-called irrigation method for saving of water. In this irrigation technology, amount of water for irrigation per dripping device is restricted to the amount as small as 0.8 L to 3 L/hour via a dripping device provided on a tube or built in the tube in view of performing the uniform irrigation for wider area. This irrigation method has been developed mainly for agricultural irrigation in the drying region, for example, in Israel and may also be used for irrigation of liquid fertilizer by mixing the desired liquid fertilizer to water.
The droplet irrigation technology is the typical irrigation technology for saving of water. However, since the amount of irrigation per dripping device is as small as 0.8 L to 3 L/hour and a dripping device is usually provided in every 20 to 30 cm, the flow rate about 10 L/min. is required for the tube length of 100 m. For the irrigation of 1 ha area, the flow rate of 1000 L/min. is required. When discharge capability of a circulating pump and capability of liquid fertilizer mixing device (having the limit of about 100 L/min.) are considered, irrigation is implemented for every small section using electro-magnetic valves and controllers. Since the pump having higher discharge capability, liquid fertilizer mixing device, electro-magnetic valve and controller having higher capability remarkably raise the cost of the irrigation system as a whole, these elements are spread only to the farmhouses in the scale of enterprises.
Moreover, when the droplet irrigation is performed for a longer period in the amount of irrigation of several liters per dripping device, here rises a problem in the flow of water and liquid fertilizer element because penetration to the deeper area of soil in the gravity direction due to the lateral penetration. Moreover, even when amount of evaporation is rather small in the rainy or cloudy days, since the irrigation instruction which totally relies on the controller is issued, it cannot always be said that irrigation and fertilization are performed depending on the required amount of farm products. Through combination with a rain-fall sensor or a soil water sensor, more accurate control can be realized but the cost further rises.
As the other profile of the irrigation technology for saving of water, a irrigation fertilization system has been proposed in which flow of water and liquid fertilizer into the deep area of soil is remarkably reduced by repeatedly performing intermittent irrigation in a small amount during a day and then effectively irrigation the liquid fertilizer only to the upper layer portion of the soil (region where group of roots of farmer products is distributed) (refer to the patent document 1 (WO98/54953). This system is provided with a plurality of local subsystems and each local subsystem is controlled with the remote control operation. Each local subsystem comprises a storage tank of the capacity to store at least the water (and liquid fertilizer) in the amount discharged during one cycle, a irrigation device for receiving a signal from the controller to control the amount of water to be irrigated and to discharge the controlled amount of water, an electronic controller to determine the frequency and time of discharging, and a tube irrigation system to guide the water to the irrigation place.
Water is supplied to the storage tank with a pump. When the storage tank is filled with water, supply of water is stopped and the tube irrigation is conducted to the wider area by opening and closing the electro-magnetic valve at the previously programmed day and time. The electric power for turning ON and OFF the control signal and opening and closing the electro-magnetic value depends on the power supplied from a solar panel to form the ecological irrigation facility. Moreover, the venturi system may be introduced for the liquid fertilizer in which concentrated liquid fertilizer can be extracted and reduced by utilizing pressure difference of water flow.
Moreover, as an automatic irrigation system utilizing the power source from the solar panel, the patent document 2 (Japanese Published Unexamined Patent Application No. 238031/1996) describes the irrigation system in which a solar battery array is installed to receive the solar beam only at the predetermined time in a day, irrigation water is pumped up from a reserving tank and is then irrigated to the green area through a irrigation hose with a DC brushless motor pump which is driven in direct with the DC output from the solar battery array. According to this automatic irrigation system, automatic irrigation at the predetermined time in a day can be realized without any complicated setting of timer.
[Patent document 1]
WO98/54953
[Patent document 2]
Japanese Unexamined Patent Publication No. 238031/1996
The droplet irrigation facility described provides various merits as the irrigation technology for saving water. However, many expensive sensors and electro-magnetic valves or control mechanisms are required to implement effective irrigation and fertilization suitable for farmer products. Moreover, a liquid fertilizer mixing device which can realize delicate control is required to mix the adequate amount of liquid fertilizer. Even in the irrigation and fertilizing system described in the patent document 1 (WO98/54953), the water stored in the storage tank can be irrigated to the wider area with the tube irrigation method through the opening and closing of the electro-magnetic valve at the programmed day and time. Therefore, in order to attain the optimum irrigation and fertilizing environment for the farmer products, high level control system is required for controlling the opening/closing timing and time of the electro-magnetic valve, resulting in rise of cost. In addition, the venturi system is employed for the liquid fertilizer to extract and reduce the concentrated liquid fertilizer by utilizing pressure difference of water flow, but it is difficult for this venturi system to obtain higher accuracy.
In the automatic irrigation system described in the patent document 2 (Japanese Published Unexamined Patent Application No. 238031/1996), the irrigation water stored in the reserving tank is pumped up for irrigation by utilizing a DC brushless motor pump which is driven in direct with a DC output generated by a solar battery array in order to realize automatic irrigation at the constant times. However, a complicated mechanism is required to install the solar battery array to receive the solar beam only at the constant times in a day. Moreover, any consideration is not taken for setting of the optimum irrigation and fertilizing environment suitable for farmer products depending on the weather condition of the day.